The normal heart is a strong, muscular pump a little larger than a fist .
The heart is the organ responsible for pumping blood throughout the body.
It pumps blood continuously through the circulatory system.
Each day the average heart "beats" (expands and contracts (systole & diastole) 100,000 (One hundred & thousand) times and pumps about 2,000 gallons (GB = 4 lit. 54 & US = 3 lit. 78) (7568.6 litres in metric system) of blood.
In a 70-year lifetime, an average human heart beats more than 2.5 billion times.

The circulatory system is the network of elastic tubes that carries blood throughout the body.
It includes the heart, lungs, arteries, arterioles (small arteries), and capillaries (very tiny blood vessels).
These blood vessels carry oxygen rich blood to all parts of the body.

The circulatory system also includes venules (small veins) and veins.
These are the blood vessels that carry oxygen depleted blood back to the heart and lungs. If all these vessels were laid end-to-end, they'd extend about 60,000 miles (96560.6 Km). That's enough to encircle the earth more than twice.

What is the heart's structure?

.The normal heart has a right side and left side, separated by a wall (septum).
Each side is further divided into an upper collecting chamber (atrium) and lower pumping chamber (ventricle).
The heart has four chambers through which blood is pumped.
Each side is further divided into an upper collecting chamber (atrium) and lower pumping chamber (ventricle).

· The upper two are the right and left atria.
· The lower two are the right and left ventricles.

A heart's four chambers must beat in an organized manner.
This is governed by an electrical impulse.
A chamber of the heart contracts when an electrical impulse moves across it.
This lets the heart rate respond to varying demands.
Normally, the right atrium receives blood returning from the body. This blood is low in oxygen, giving it a bluish color. It flows to the right ventricle, and is then pumped out of the pulmonary artery to the lungs. In the lungs it picks up fresh oxygen and becomes bright red. This "red blood" then flows through the pulmonary veins to the left atrium and into the left ventricle. It is then pumped out of the aorta to the rest of the body, delivering oxygen and nutrients. Once oxygen is delivered to and extracted by the body tissues, the "blue blood" returns through the veins to the right atrium, beginning the cycle again.

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